This invention relates to an implantable cardiac defibrillator circuit, and more specifically, to a power supply contained therein comprising a capacitively coupled bridge circuit for using a low-voltage circuit section to control a high-voltage circuit section while maintaining isolation between the high- and low-voltage sections.
In many electronic systems a low voltage source is often needed to control a corresponding high voltage source. One such need, for example, is commonly found in a device known as an Implantable Cardiac Defibrillator (ICD), in which a high voltage pulse is controlled by a low voltage integrated circuit (IC). In many instances, delivery of the higher voltage is accomplished by way of a non-complementary high voltage switching matrix encompassing a bridge configuration. This switching element frequently employs N-channel Metal-Oxide Semiconductor Field Effect Transistors (MOSFETs), or Insulated Gate Bipolar Transistors (IGBTs), or Silicon Controlled Rectifiers (SCR) depending on the design specifications.
In order to enhance the overall performance of a system that involves low-to-high voltage transfer, isolation between both the voltage-generating and voltage-delivering functions is crucial. In a bridge or a switching matrix configuration having N-Channel MOSFETs or IGBTs, for instance, the transistor gate voltage needs to be higher than, or independent of, the switching voltage. The low voltage section of the system cannot, therefore, be used to provide the gate voltage directly. Therefore, an alternative method of maintaining and transferring the necessary gate voltage must be implemented.
In the art, two known methods are used to achieve level shifting and input-to-output isolation. The first involves using a transformer in combination with a full-wave bridge rectifier circuit; the other involves circuits using opto-couplers.
Although transformers combined with diode rectifiers may be adequate for shifting voltage levels, design considerations limit their use in certain situations. First, transformers are bulky, and hence, are unsuitable in certain applications where minimizing the three-dimensional space of the device is critical, such as in an ICD. Similarly, transformers are discrete devices, and thus, cannot be incorporated in a CMOS integrated circuit (IC).
Opto-couplers, on the other hand, suffer from the same size impediments as isolation transformers. Moreover, in dual- or multi-channel design applications, optocouplers are susceptible to signal distortion and cross talk.
Accordingly, a power supply that delivers a high power output controlled by low power input while simultaneously capacitively isolating the two sources would be advantageous. Such a device would also have the advantage of being readily integrated into standard CMOS IC production processes. The performance characteristics and small size of IC embodiments of such a device would be particularly advantageous for use in small-size applications such ICD""s.
The invention provides a power supply with integral control circuit for providing a low-voltage control signal with capacitive coupling to a high-voltage section having an output for powering a load. The power supply is adapted to operate the high-voltage section in response to a signal from the low-voltage section.
According to one aspect of the invention, the integral control circuit and capacitive coupling are implemented as a single IC.
According to another aspect of the invention, the integral control circuit is implemented as a full bridge rectifier driver circuit.
Embodiments of the invention disclosed include implantable cardiac defibrillator circuits where a bridge section capacitively couples the low-voltage section to the high-voltage section.
The invention provides several technical advantages over the prior art. The capacitive coupling used by the invention is smaller and less expensive to implement than isolation devices used in the arts. The remainder of the accompanying bridge circuit provides advantages in terms of operational characteristics, manufacturing techniques, and size. The invention is particularly advantageous for use in applications concurrently demanding fast response, a high degree of portability, and reliable isolation of high- and low-voltage circuit components. One example of such an application is an implantable cardiac defibrillator. Further advantages will become apparent to those skilled in the arts upon review of the following description, figures and claims.